Inflation systems for deploying an air bag in a motor vehicle generally employ a single gas generator in fluid communication with an uninflated air bag. A firing circuit typically triggers the gas generator when the sensed vehicle acceleration exceeds a predetermined threshold value, as through the use of an acceleration-responsive inertial switch.
However, air bag inflation systems utilizing a single gas generator suffer from the disadvantage that the onset pressurization/inflation rate is generally set to provide aggressive initial inflation in order to achieve a particular inflation time related to occupant position. An aggressive onset rate of pressurization becomes problematic in situations where the occupant is out of position. More specifically, rapid onset pressurization of the air bag may cause the air bag to impact against the occupant with a greater force than necessary. In essence, the airbag volume and inflating capacity are designed to protect both large and small occupants and are generally not variable within the single gas generator. Occasionally, when an air bag utilizing a single gas generator is deployed, smaller occupants, usually children and smaller adults are protected, but sometimes with more force than is necessary. Accordingly, there is a continuous drive to reduce the force acting upon a respective occupant to a tailored force rather than utilizing a generalized force that protects all sizes of occupants.
Commonly owned U.S. Pat. No. 5,400,487 discloses an inflation system that overcomes the above problem by utilizing a plurality of gas generators which are controllably ignited to provide a variable inflation profile which can be tailored to any given occupant weight and/or position and for any crash type. While this arrangement dramatically improves the inflation system's ability to protect an occupant, it does so at significant expense and complexity. The multiple gas generators and squibs add considerable cost to the system, while the firing control circuitry requires sophisticated processors capable of accurately timing the various ignition profiles.
Another proposal, as taught in commonly owned U.S. Pat. No. 5,934,705, is a gas generator having two chambers in a single housing defined by a mechanically retained wall between the ends thereof. Each housing is of a predetermined size that is determinative of the propellant capacity and consequently, of the inflating capability of each chamber. Upon the occurrence of a vehicle collision, depending on the weight of the passenger, either chamber or both may be selectively ignited thereby inflating the protective airbag. However, this design appears to accommodate passenger-side inflators only.
Other known designs employ multiple chamber inflators wherein the chambers are sized to different dimensions and volumes. As such, each chamber retains a relatively greater or lesser amount of gas generant depending on its size. Based on data gathered by an associated system algorithm, the size and/or position of the occupant is then determinative of what chamber or chambers are employed thereby resulting in a greater or lesser airbag restraining force. One concern is that this approach necessarily complicates the manufacturing process in that the inflator contains additional parts. Also, the system algorithm employed to process the occupant size and/or position data is necessarily more complex in that more choices or outcomes are required to accommodate the various permutations or combinations of firing the various chambers.
Therefore, a need exists for a multiple chamber gas generator that exhibits a simplified design, simplified manufacturing, and therefore lower material and manufacturing costs, and yet can still produce selective air bag inflation pressurization.